全文获取类型
收费全文 | 23212篇 |
免费 | 3499篇 |
国内免费 | 2516篇 |
专业分类
化学 | 16422篇 |
晶体学 | 281篇 |
力学 | 1358篇 |
综合类 | 190篇 |
数学 | 2347篇 |
物理学 | 8629篇 |
出版年
2024年 | 68篇 |
2023年 | 431篇 |
2022年 | 753篇 |
2021年 | 834篇 |
2020年 | 874篇 |
2019年 | 854篇 |
2018年 | 726篇 |
2017年 | 746篇 |
2016年 | 1031篇 |
2015年 | 1052篇 |
2014年 | 1186篇 |
2013年 | 1635篇 |
2012年 | 1905篇 |
2011年 | 2017篇 |
2010年 | 1319篇 |
2009年 | 1286篇 |
2008年 | 1483篇 |
2007年 | 1375篇 |
2006年 | 1242篇 |
2005年 | 1003篇 |
2004年 | 782篇 |
2003年 | 677篇 |
2002年 | 642篇 |
2001年 | 474篇 |
2000年 | 468篇 |
1999年 | 503篇 |
1998年 | 439篇 |
1997年 | 435篇 |
1996年 | 475篇 |
1995年 | 380篇 |
1994年 | 391篇 |
1993年 | 276篇 |
1992年 | 257篇 |
1991年 | 235篇 |
1990年 | 166篇 |
1989年 | 129篇 |
1988年 | 117篇 |
1987年 | 98篇 |
1986年 | 96篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
本文讨论了29个不对称色酸双偶氮膦酸型显色剂的分子联接性指数,并将其与结构选择性因子相结合,用于偶氮类剂结构与铈显色反应灵敏度的相关性研究,讨论了显色剂结构对显色反应灵敏度的影响。 相似文献
142.
143.
144.
The effect of pressure during thermal plasma chemical vapor deposition of diamond films has been investigated for a pressure range from 100 to 760 Torr. The maximum growth rate in our experiments occurs at 270 Torr for substrate temperatures around 1000°C. The existence of an optimum pressure for diamond deposition may he related to the balance between generation and recombination of atomic hydrogen and carbon-containing active species in front of the substrate. To estimate the concentrations of atomic hydrogen and methyl radicals under thermal plasma conditions, calculations based on thermodynamic equilibrium have been performed. This approximate evaluation provides useful guidelines because rapid diffusion results in a near frozen chemistry within the boundary layer. The effect of substrate pretreatment on diamond deposition depends on the type of substrate used. Two growth modes have been observed-layer growth and island growth of diamond crystals on various substrates. Screw dislocations have been observed in diamond deposition in thermal plasmas, and defects such as secondary nucleations are more concentrated along (III) directions than along (100) directions. 相似文献
145.
Ye Qing Li Ming Lu Chun Xu Lu Sai Jian Zhu Qi Fa Liu 《中国化学快报》2007,18(11):1313-1315
A novel and simple procedure for synthesis of azanucleoside by Mitsunobu reaction between N-(p-nitrobenzyloxycarbonyl)- trans-4-hydroxy-D-proline methyl ester obtained from trans-4-hydroxy-L-proline after six-step reaction and 2-fluoro-6-azidopurine is described,and azanucleoside is fluorinated by new fluridizer 2,2-difluoro-1,3-dimethylimidazolidine (DFI).All reactions could be carded out under mild condition. 相似文献
146.
Yuanyuan Han Qinghai Cai Bin Lu Xue Xiao Shuhan Cui 《Reaction Kinetics and Catalysis Letters》2007,91(1):29-35
A novel solid acid prepared from concentrated sulfuric, boric and phosphoric acid is a highly selective catalyst for the dimerization
of α-methylstyrene at room temperature to generate 4-methyl-2,4-diphenyl-1-pentene. 相似文献
147.
Huang M Jin Y Jiang H Sun X Chen H Liu B Wang E Dong S 《The journal of physical chemistry. B》2005,109(32):15264-15271
Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost. 相似文献
148.
149.
150.
A method is proposed to calculate molar conductivity based on mode coupling theory in which the ion transference number is introduced into the theory. The molar conductivities of LiPF6, LiClO4, LiBF4, LiAsF6 in PC (propylene carbonate) are calculated based on this method. The results fit well to the literature data. This presents a potential way to calculate the conductivities of Li-ion battery electrolytes. 相似文献